It becomes necessary for an image sensor utilizing an illuminating apparatus of a line light source applied to an image reader apparatus to ensure uniform light emission in a main scanning direction (a lengthwise direction), and a reading depth (a focal depth) in accordance with an improvement of a resolution. Example conventional technologies known are as follows. Patent Literature 1 discloses a mechanism in which an optical housing secures a liquid crystal element.
In addition, FIG. 1 of Patent Literature 2 discloses an illuminating apparatus that causes a lighting element to emit light through an end face of a cylindrical light guide that is long in the main scanning direction to uniformly emit light in the scanning direction. More specifically, the light guide and a lighting element board on which the lighting element is mounted are attached to a holder, and are positioned relative to each other. This holder is secured to a frame by engagement pins provided at both end faces of the holder in the sub scanning direction (a shorter direction) and a positioning hole formed in a wall of the frame. Note that an example image sensor of Patent Literature 2 is a contact image sensor (CIS).
Still further, in accordance with an increase of an output by a light source applied to an illuminating system of a contact image sensor, an efficient heat radiation structure for a light source is necessary. FIG. 4 of Patent Literature 3 discloses that an LED chip that is a light source is mounted on a metal plate, and a bent heat radiation plate is attached to a planar portion at an opposite face side of the LED chip to perform heat radiation on the light source.